Viroids and Prions

by Jason Amores Sumpter
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I know at the beginning of the lesson I was going on and on about how small viruses are. Well it turns out they're actually not the smallest infectious pathogens. There are actually smaller infectious agents known as Vai roids. And these are actually the smallest pathogen known and they consist of a short circular single stranded piece of RNA pictured right here. This is an actual image of a viral oid. And you can see it starts with this c base pair right here, labeled one. You can see the one right there, it goes all along this way, there is some base pair binding as it folds back in on itself. You can see there's these stretches of base pair binding. I'm kind of just running my pen through those bonds. It's almost like I'm cutting them and so it folds back in on itself and ends with base 359. So this is not even 500 bases long. This is a teeny stretch of RNA And yet this is a pathogen. It infects Vai Roids infect mostly plants and they tend to disrupt plant growth. So plants infected with virus roids tend to be short or stubby or malformed because they their growth is somehow disrupted. Now Vie Roids do not actually encode proteins like viruses. They simply replicate themselves using the hosts enzymes and this uh self replication ultimately leads to problems for the host and propagation of the virus roids. So kind of similar idea to viruses there. Now there are actually other teeny infectious agents called prion. Now, these are bigger than Vai roids. They're actually proteins and these instead of affecting plants tend to affect animals, specifically the brain tissue of animals. The way prions work, you can kind of think of a prion as a weirdly folded protein. And essentially these weirdly folded proteins can interact with normal proteins that have their proper folded form and cause them to get all misfolded and bent out of shape. So in that sense they self propagate misfolding in other proteins. And we can see a little simplified diagram of that happening right here. So here these green balls that's the proper fold for the protein. It interacts with this weird fold in this protein seen in red with little spiky balls around the outside and that causes see the green properly folded protein ends up being misfolded as we see there and this leads to an accumulation of these misfolded proteins. And protein gunk build up in nerve cells is actually very, very toxic and harmful to the nerve cells causes nerve cell death. In fact, protein like garbage protein build up is also implicated in diseases like Alzheimer's as the cause for cell death in those diseases. So building up garbage protein might not sound like it's that bad actually very harmful for cells. So that's how these pry UN's can actually cause a lot of cell death in the brain and lead to a variety of diseases. Now that's all I have for this lesson. I'll see you guys next time